Past climate change - Climate Change: Biological and Human Aspects - page 88

in diminished photosynthesis and cooling on a global scale for several years (not
to mention spectacular sunsets). As with the end-Permian extinction, a fungal and
algal spike has been identified (Vajda and McLoughlin, 2004). This was followed by
a recovery led by pteridophytes and gymnosperms (ferns and seed-bearing/woody
plants). The Cretaceous-Tertiary and end-Permian vegetation recoveries represent
similar responses to terrestrial ecosystem collapse, although the end-Permian bio-
diversity crisis was much more prolonged. Whether or not there was a subsequent
warming period depends on how much carbon dioxide was released. Either way, a
change in the climate, albeit for a few years, would have been the main cause of
the dinosaur extinction worldwide, although on a continental basis there would have
been shock events and raining ejecta, causing life to be wiped out. Here endeth the
summarystory...well,notquite.
There are still some who say that an asteroid did not wipe out the dinosaurs. As
a point of pedantry this view has much merit. To begin with, only some genera of
dinosaurs became truly extinct. Other genera only suffered a pseudo-extinction: they
did not die out as such but new species evolved. For example, birds evolved. Second,
the dinosaurs were already in decline prior to the asteroid impact. The 60-million-
year-long Cretaceous period was the third period (the Triassic and Jurassic being the
other two) in the Mesozoic era of the dinosaurs, beginning 251 mya. The Mesozoic
saw considerable evolution in the dinosaurs, and some dinosaur species that were
around in the Triassic (at the beginning of the Mesozoic) were not around in the
Cretaceous. Conversely, some dinosaurs did not evolve until the Cretaceous. Indeed,
the Tyrannosaurus rex star of the topic (and film) Jurassic Park is associated with
the Cretaceous, not the Jurassic. Overall, many dinosaur genera were in decline well
before the end of the Cretaceous and its asteroid impact, and so the asteroid cannot
have been responsible. The possible culprit behind the - if you will - pre-asteroid
dinosaur decline may well be the considerable volcanic activity associated with the
Deccan Traps in north-west India. The Traps represent the remains of a continental
flood basalt event (like the end-Permian Siberian Traps) which is thought to have
been active (albeit to varying degrees) for 8 or 9 million years somewhere around
60-65 mya, although there are some associated geological events that occurred earlier
than this (70 mya). The continental flood basalt event would have released cooling
dust and ash as well as warming carbon dioxide and methane. Either way, a global
impact of the continental flood basalt event was virtually unavoidable. As such, this
combination of volcanic traps and an asteroidal impact is possibly similar to the end-
Permian extinction, although the blame for the end-Permian event lies more firmly
with the vulcanism of the Siberian Traps. What may have happened in the Cretaceous
is that the Deccan Traps flood basalt event, which lasted many millions of years,
altered the biosphere sufficiently to stress dinosaurs, and then the end-Cretaceous
asteroid impact provided the coup de gr ace .
Then again, the dinosaurs were not the only life on Earth at that time: indeed,
there were other newcomers. The late Cretaceous and the early Tertiary were periods
of vegetation change due to the appearance, and then increasing dominance, of
flowering plants (angiosperms). There is also evidence of a fungal spike similar to
that found associated with the end-Permian extinction. In all likelihood fungi would
have flourished in a world of much dead and rotting biomass.